1. Field of the Invention
The present invention relates to an optical film and a manufacturing method therefor, and particularly relates to the optical film provided with a hard coat, which is used as a protective layer of a polarizing plate of a liquid crystal television or monitor, and the manufacturing method therefor.
2. Description of the Related Art
The optical film provided with the hard coat is occasionally used as a protective layer of a polarizing plate and the like of a liquid crystal monitor or television, which is one of applications. In this case, when the polarizing plate is manufactured, the optical film is subjected to saponification treatment for securing adhesiveness to an adhesive, and then is laminated with the polarizer by the adhesive.
The optical film provided with the hard coat to be thus used as the protective layer of the polarizing plate of a liquid crystal television or monitor generates such a curl that the liquid-applied face side becomes inside, due to the curing and shrinking of the hard coat layer by irradiation with an active beam, which has been a cause of the decrease of the product yield due to meandering during transportation, a displacement of a laminated position and the involvement of bubbles occurring when the polarizing plate is formed.
Then, Japanese Patent Application Laid-Open No. 2004-101883 and Japanese Patent Application Laid-Open No. 2008-310343 provide a method of reducing the curl by providing a back coat layer in the opposite side of the surface having the hard coat applied thereon, as the preventive measures.
Japanese Patent No. 4011911 also discloses a method of reducing the curl by exposing the outside surface of the curl to vapor.
However, there has been a problem that the optical film adjusted to the state of having no curl by using the methods of the above three documents results in causing the curl so that the surface side having the hard coat layer applied thereon becomes inside, when a tension has been applied to the optical film in the longitudinal direction during the transportation when the optical film is laminated with the polarizer. This problem has become much more remarkable due to the tendency of the width increase and thinning of the optical film, and has been a cause of poor transportation precision and the involvement of bubbles.